US5849060A - Controlled release fertilizer and preparations thereof - Google Patents

Controlled release fertilizer and preparations thereof Download PDF

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US5849060A
US5849060A US08/695,386 US69538696A US5849060A US 5849060 A US5849060 A US 5849060A US 69538696 A US69538696 A US 69538696A US 5849060 A US5849060 A US 5849060A
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fertilizer
compounds
soluble
coating layers
limited
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Li Diping
Wang Haobin
Xu Xiucheng
Hou Cuihong
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Zhengzhou Centre of Populariz'n and Res on Phosphate and Fertilizer
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Assigned to ZHENGZHOU CENTRE OF POPULARIZATION & RESEARCH ON ZHENGZHOU LUXURIANCE PHOSPHATE & COMPOUND FERTILIZER reassignment ZHENGZHOU CENTRE OF POPULARIZATION & RESEARCH ON ZHENGZHOU LUXURIANCE PHOSPHATE & COMPOUND FERTILIZER ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HOU, CUIHONG, LI, DIPING, WANG, HAOBIN, XU, XIUCHENG
Assigned to ZHENGZHOU CENTRE OF POPULARIZATION & RESEARCH ON ZHENGZHOU LUXURIANCE PHOSPHATE & COMPOUND FERTILIZER reassignment ZHENGZHOU CENTRE OF POPULARIZATION & RESEARCH ON ZHENGZHOU LUXURIANCE PHOSPHATE & COMPOUND FERTILIZER DUPLICATE RECORDING, SEE RECORD ON REEL 9163, FRAME 0990. Assignors: HOU, CUIHONG, LI, DIPING, WANG, HAOBIN, XU, XIUCHENG
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    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G1/00—Mixtures of fertilisers belonging individually to different subclasses of C05
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G5/00—Fertilisers characterised by their form
    • C05G5/30—Layered or coated, e.g. dust-preventing coatings

Definitions

  • the present invention relates to a controlled release fertilizer and the methods for preparing the same.
  • a controlled release fertilizer is a kind of compound fertilizer which can control the release of plant nutrients therefrom.
  • Sulfur coated fertilizer was first developed by U.S.A in 1961, and came into commercial production in 1978. In 1990, the output of the fertilizer in the world had amounted to 115,000t which was below 0.2 percent of the amount of the total urea output in the world. In 1975, the sulfur coated compound fertilizer was developed by Japan; and in 1981, sulfur coated potassium chloride and sulfur coated potassium sulfate fertilizers were developed by O. M. SCOTT, U.S.A. Processes for coating sulfur are very complicated in that melted sulfur is first coated on the surfaces of urea granules, and then the sulfur coated surfaces are sealed with melted paraffin wax. The weakness of this kind of fertilizer is that the nucleus of the fertilizer is released out very quickly and that the coated wax is easy to be decomposed by microorganisms in the soil, as a result of which the controlled release effect is disadvantageously affected.
  • the coating layer of a resin coated slow release fertilizer represented by the OSMOCOTE® U.S.A is essentially composed of a copolymer of cyclopentadiene dimer and glyceride, the amount of the coating layer is at a level of about 10-15% wt of the total weight of fertilizer.
  • the resin coated slow release fertilizer has excellent controlled release properties. The contained plant nutrients can be controlled to release out 80% of the nutrients in 120-360 days.
  • a coated compound fertilizer was disclosed in China Patent CN 851010089 which comprises the granular urea or ammonium nitrate as nucleus coated with a fertilizer selected from FMP (fused magnesium phosphate ), precipitated calcium phosphate and bone powder, with the use of nitrogen phosphorus slurry as binders.
  • FMP fused magnesium phosphate
  • precipitated calcium phosphate precipitated calcium phosphate and bone powder
  • a slow release coated fertilizer is disclosed in Chinese Patent CN89102295, which comprises using vegetable oils, animal oil or their greases or their modified substances as a retarder in the coating layer so that the release time of nutrients in the nucleus can be prolonged to 15-30 days, by this way, the release of nutrients in the nucleus can be retarded.
  • Chinese Patent CN89102295 which comprises using vegetable oils, animal oil or their greases or their modified substances as a retarder in the coating layer so that the release time of nutrients in the nucleus can be prolonged to 15-30 days, by this way, the release of nutrients in the nucleus can be retarded.
  • solubilities of the limited-soluble compounds can be changed, and release rate of nutrients can be controlled so as to satisfy with the desire of plants in different growing stages.
  • the present invention provides a controlled release fertilizer with water-soluble fertilizer(s) as nucleus and limited-soluble plant nutrients as coating layers, characterized in that coating layers of limited-soluble compounds are formed around the nucleus, and that release rates of the nutrients can be controlled by regulating the solubilities of the limited-soluble compounds.
  • the present invention also provides methods for preparing the abovementioned fertilizers, which comprise the following steps mainly:
  • FIG. 1 shows the structure of coating layers under a scanning electron microscope.
  • FIG. 2 represents X-ray diffraction spectrum.
  • FIG. 3 shows the nitrogen releasing curve of the fertilizers produced according to examples 1 and 2.
  • the coating layer of the controlled release fertilizer according to the present invention can be formed by using a mixture of sulfuric acid or phosphoric acid at certain concentrations with monoammonium phosphate (MAP); diammonium phosphate (DAP) or ammonium bicarbonate as binders to coat with compounds with various solubilities on the surface of water-soluble granular fertilizers layer by layer; or by using reactive binders to coat with compounds containing nitrogen, phosphorus, potassium, magnesium and trace element on the surface of water-soluble fertilizers, during which period limited-soluble compounds are formed in the form of several coating layers.
  • Water-proof substances such as silicone or calcium carbonate stearate can be added into the coating layers to enhance the hydrophobicity.
  • reactive magnesium oxide or phosphate rock powder can be added to form fine and close shells.
  • the present invention also provides use of the controlled release fertilizers in lawns (especially golf course) and ornamental plant.
  • the present invention is accomplished by the following procedures:
  • M is K, Na or NH 4
  • M' is Mg, Ca, Zn, Mn, Cu or Fe.
  • compositions of these compounds are shown in Table 1.
  • the compounds in Table 1 are all known compounds.
  • Compounds 1-9 in Table 1 can be prepared by phosphoric acid, sulfuric acid, magnesium oxide, magnesium carbonate, calcium oxide, ammonium phosphate, calcium carbonate, ammonium bicarbonate, zinc sulfate, manganese sulfate, potassium chloride or potassium sulfate according to literatures (such as "Inorganic Chemical Compound Synthesis Handbook” Vol. 1-2, edited by Japanese Chemistry Society, "The production and application of phosphates", pages 112-372).
  • a coating material of a controlled release fertilizer which contains nitrogen 10.2 wt %, P 2 O 5 45.9 wt %, MgO 26.2 wt % ("Phosphate and Compound fertilizer", No.4, pp19-20, 1989).
  • Compounds 10-12 in Table 1 are commercially available products and compound 13 is formed by the absorption of carbon dioxide in air on magnesium hydroxide.
  • the plant nutrients, such as nitrogen, phosphorus, potassium, magnesium, zinc and manganese contained in the above compounds with limited solubilities in water can be slowly released in water.
  • the coating layers composed of the above compounds are in an amount of 35 to 68 percent on the basis of the total weight of the fertilizer.
  • the binders used comprise non-reactive binders and reactive binders.
  • the non-reactive binders can be a mixture of sulfuric acid or phosphoric acid at certain concentrations with monoammonium phosphate, diammonium phosphate or ammonium bicarbonate, which mixture is bound with compounds having various solubilities and coated on the surface of water-soluble granular fertilizer layer by layer.
  • the binders can be reactive binders which can react with single fertilizer such as urea, monoammonium phosphate, diammonium phosphate, ammonium bicarbonate, ammonium sulfate, potassium chloride or potassium sulfate to form limited-soluble compounds .
  • Two kinds of reactive binders can be selected, one kind is organic binders such as formaldehyde, starch and carboxy methyl cellulose, which can condense with urea to form limited-soluble compounds containing nitrogen.
  • Urea has a property of condensation-addition with various organic compounds (UREA, ITS PROPERTIES AND MANUFACTURE).
  • FIG. 1 An example is taken for illustrating the condensation reaction of urea with formaldehyde. 0.04 kg hexamethyleneamine was added to 3kg formaldehyde solution (37 wt %), after completely dissolved, 0.8 kg urea was added with continuously stirring and heating until said urea was completely dissolved. The mixture was heated to a constant temperature of 60° C.
  • the other kind of binders is inorganic binders such as phosphoric acid or sulfuric acid used alone or mixed with monoammonium phosphate, diammonium phosphate, ammonium bicarbonate or ammonium sulfate, said binders can react with magnesium oxide, calcium oxide, zinc sulfate, manganese sulfate, potassium sulfate or potassium chloride to obtain compounds 1-9 in Table 1.
  • concentrations and formulations of the selected binders are shown in Table 2.
  • the amount of the binders is 5-10% on the basis of the total weight of fertilizer.
  • the solubilities of limited-soluble compounds 1-10 in Table 1 can be adjusted by adding inorganic additives such as ammonium sulfate, ammonium chloride, ammonium nitrate and magnesium sulfate into the coating layer and the release rates of nutrients in the fertilizer can be controlled.
  • the amount of regulator is 0-5% on the basis of the total weight of fertilizer.
  • the solubility of MgNH 4 PO 4 .6H 2 O in Table 1 can be adjusted by adding ammonium sulfate as shown in Table 3. When no ammonium sulfate is added, 80% nitrogen in the fertilizer can be released out within 140 days. If adding 5% ammonium sulfate, the release period is only 70 days.
  • the solubilities of the limited-soluble compounds can also be changed by adjusting the pH values of the salts contained in the coating layers so as to control the release rates of the fertilizers.
  • the solubilities of FMP listed in Table 1 will change along with the pH values of the solutes, as shown in Table 4.
  • the dissolution condition i.e. the pH value is controlled to be more than 7 to decrease the solubilities of the limited soluble compounds in Table 1 and thus prolong the release time of nutrients.
  • the pH value of the solution is less than 7, then the release of the nutrients can be accelerated.
  • the toppest layer of the coating layers can increase the density of the coating layers and decrease the hydrophilicity of the coating layers. Therefore, powder is applied on the surface of the coating layer.
  • the powder used comprises fine magnesium oxide powder( ⁇ 0.075 mm), which absorbs carbon dioxide from air to form compound 13 in Table 1 with smooth and fine shells.
  • a calcium carbonate stearate powder (a water proof and insulated powder material whose preparing method can be found in Chinese Patent CN 91105131.7) is applied or a organic silicone is coated on to form a hydrophobic layer.
  • the amount of the powder and hydrophobic layer applied is 2-5% by weight of the total fertilizer.
  • the controlled release fertilizer according to the present invention can be manufactured by using granular water-soluble fertilizer such as urea, ammonium nitrate monoammonium phosphate, diammonium phosphate, potassium chloride, potassium sulfate and other compound fertilizer as nucleus, and coating on the nucleus with compounds containing nitrogen, phosphorus, potassium, magnesium and trace elements and having different limited solubilities layer by layer; or coating on the nucleus with limited soluble compounds which are formed by the reaction between a reactive binder and a single fertilizer during coating process.
  • the number of coating layers are not less than 2, and preferable 3-5 so that the coating layers have a desirable thickness and different release rate.
  • the solubility of limited-soluble compound can be changed by regulating the composition and pH value of coating layers, by which nutrient-releasing rate can be controlled to a release period of 60-240 days (the time required to release 80% nutrients).
  • a controlled release fertilizer containing 30-50 wt % nitrogen, phosphorus pentoxide, potassium oxide and magnesium oxide can be manufactured optionally. Analysis with a scanning electroscope found that the cross section of coating layers was composed of dense amorphous compounds.
  • the controlled release fertilizer is essentially composed of nucleus and coating layers, the amount of nucleus is 20-50% by weight of the total mass, while the amount of coating layer is 50-80% by weight of the total mass.
  • the coating layer is comprised of a limited-soluble compound, an adjustment agent, a powder and a binder, which are 35-70%, 0-5%, 2-5% and 5-10% by weight of the total fertilizer respectively most of which are plant nutrients.
  • the coating layer contained MgO, NH 4 MgPO 4 .6H 2 O, Mg(OH) 2 , KMgPO 4 .6H 2 O, KCaPO4.H 2 O (see FIG. 2).
  • the second coating layer was formed by coating 16 parts synthesized KMgPO 4 .H 2 O onto the granules having the first coating layer by means of binder OB, which was 17.7% by weight of the total fertilizer.
  • the third coating layer was formed by coating with 16 parts FMP by means of 30 wt % sulfuric acid as binder, which was 18% by weight of the total fertilizer.
  • a fine and close shell layer was formed by powdering on the surface of the fertilizer with 4 parts magnesium oxide powder. The final product was dried at 70 C until the water content was less than 2%, and then packed up after cooling to obtain a fertilizer containing N 13%, P 2 O 5 18%, K 2 O 5% and MgO 3%.
  • the release rate of the fertilizer in soil was determined as follow:
  • a ⁇ 75 ⁇ 9 cm plastic pot was filled with a simulated soil which was composed of equal parts by volume of vermiculite powder and peat in a particle-size less than 10 mesh. There were several dozens of ⁇ 3 mm drainage holes at the bottom of the pot.
  • the fertilizer sample of example 2(3 g) was incorporated uniformly into the simulated soil.
  • the medium was then surface irrigated with distilled water until the medium was nearly saturated, but with little or no leaching from the pot.
  • the whole installation was sealed and held at a constant temperature of 20° C. After a period of time, the saturated solution was extracted and analyzed for the N content, and resaturated with distilled water. The various release rates at different time can be measured in this way.
  • the release rates curves was shown in FIG. 3.
  • the Fertifizer provides 60, 90, 120 days longevity for nitrogen releasing, high utilization ratio of fertilizer, less frequent application and reduced labor costs;
  • the fertilizer of the invention can be widely used in the fairways, roughs, parks, race courses, lawn tennis courts, sport grounds, turf farms and lawns.

Abstract

The present invention relates to a controlled release fertilizer having water-soluble fertilizers as nucleus and limited-soluble plant nutrient compounds as coating layers, characterized in that more than two coating layers of limited-soluble compounds are formed around the nucleus, and that the release rates of the fertilizer can be controlled by regulating the solubilities of the limited-soluble compounds. The invention also relates to a process for preparing the controlled release fertilizer.

Description

FIELD OF THE INVENTION
The present invention relates to a controlled release fertilizer and the methods for preparing the same.
BACKGROUND OF THE INVENTION
A controlled release fertilizer is a kind of compound fertilizer which can control the release of plant nutrients therefrom.
Nowadays, people have paid more attention to development of various kinds of compound fertilizer so that the plant nutrients contained can be slowly released within a required time, and that the release rate can be consistent with rates of plants absorption during their growing stages. Since 1960s, various coated fertilizers have been developed in U.S.A, Japan, England, France etc., of which sulfur coated fertilizer and resin coated fertilizer are two of the main types.
Sulfur coated fertilizer was first developed by U.S.A in 1961, and came into commercial production in 1978. In 1990, the output of the fertilizer in the world had amounted to 115,000t which was below 0.2 percent of the amount of the total urea output in the world. In 1975, the sulfur coated compound fertilizer was developed by Japan; and in 1981, sulfur coated potassium chloride and sulfur coated potassium sulfate fertilizers were developed by O. M. SCOTT, U.S.A. Processes for coating sulfur are very complicated in that melted sulfur is first coated on the surfaces of urea granules, and then the sulfur coated surfaces are sealed with melted paraffin wax. The weakness of this kind of fertilizer is that the nucleus of the fertilizer is released out very quickly and that the coated wax is easy to be decomposed by microorganisms in the soil, as a result of which the controlled release effect is disadvantageously affected.
The coating layer of a resin coated slow release fertilizer represented by the OSMOCOTE® U.S.A is essentially composed of a copolymer of cyclopentadiene dimer and glyceride, the amount of the coating layer is at a level of about 10-15% wt of the total weight of fertilizer. The resin coated slow release fertilizer has excellent controlled release properties. The contained plant nutrients can be controlled to release out 80% of the nutrients in 120-360 days.
The common disadvantage of the above-said two types of coated fertilizers is that they are expensive. For example, according to U.S.A market price in 1994, the price of SCU was 1.7 times as much as that of the urea, and the resin coated fertilizer was 8.2 times as much as that of the urea.
On the other hand, a coated compound fertilizer was disclosed in China Patent CN 851010089 which comprises the granular urea or ammonium nitrate as nucleus coated with a fertilizer selected from FMP (fused magnesium phosphate ), precipitated calcium phosphate and bone powder, with the use of nitrogen phosphorus slurry as binders.
This kind of fertilizer whose cost is greatly decreased with the use of fertilizer coated with fertilizer, was honored as "the cheapest slow release fertilizer came from China" by an international magazine ("Nitrogen", No. 191, pages 35-41, May-Jun., 1991). The price of the fertilizer in China is only 75 percent of that of urea. However, under the electronic microscope, the coating layer of the fertilizer observed shows a slice structure with many large and small holes and cracks on surfaces of the fertilizer, which can not prevent water from penetrating the coating layer effectively. When soaked in water, the coated urea and ammonium nitrate in the nucleus of the fertilizer will be dissolved out completely in 1.5-2.0 hours so that a good controlled release effect can not be achieved.
As an improvement a slow release coated fertilizer is disclosed in Chinese Patent CN89102295, which comprises using vegetable oils, animal oil or their greases or their modified substances as a retarder in the coating layer so that the release time of nutrients in the nucleus can be prolonged to 15-30 days, by this way, the release of nutrients in the nucleus can be retarded. But there are some shortcomings:
a. The release of water soluble potassic fertilizer can not be retarded.
b. Adding so many retarders which are not plant nutrients into fertilizer will affect the total nutrient content in the fertilizer,
c. Adding retarders alone can not control the release rate of nitrogen, phosphorus and potassium freely.
It is therefore an object of the present invention to provide a type of compound fertilizer composed of compounds containing nitrogen, phosphorus, potassium, magnesium and trace elements with various release rates. By regulating the structure and the composition of the coating layers, solubilities of the limited-soluble compounds can be changed, and release rate of nutrients can be controlled so as to satisfy with the desire of plants in different growing stages.
It is another object of the invention to provide a method for preparing said controlled release fertilizer.
SUMMARY OF THE INVENTION
The present invention provides a controlled release fertilizer with water-soluble fertilizer(s) as nucleus and limited-soluble plant nutrients as coating layers, characterized in that coating layers of limited-soluble compounds are formed around the nucleus, and that release rates of the nutrients can be controlled by regulating the solubilities of the limited-soluble compounds. The present invention also provides methods for preparing the abovementioned fertilizers, which comprise the following steps mainly:
a) selecting one or more fertilizer(s) as nucleus;
b) coating with limited soluble compounds on said nucleus to form at least two coating layers by means of a binder.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the structure of coating layers under a scanning electron microscope.
FIG. 2 represents X-ray diffraction spectrum.
FIG. 3 shows the nitrogen releasing curve of the fertilizers produced according to examples 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION
The coating layer of the controlled release fertilizer according to the present invention can be formed by using a mixture of sulfuric acid or phosphoric acid at certain concentrations with monoammonium phosphate (MAP); diammonium phosphate (DAP) or ammonium bicarbonate as binders to coat with compounds with various solubilities on the surface of water-soluble granular fertilizers layer by layer; or by using reactive binders to coat with compounds containing nitrogen, phosphorus, potassium, magnesium and trace element on the surface of water-soluble fertilizers, during which period limited-soluble compounds are formed in the form of several coating layers. Water-proof substances such as silicone or calcium carbonate stearate can be added into the coating layers to enhance the hydrophobicity. And outside the coating layers reactive magnesium oxide or phosphate rock powder can be added to form fine and close shells. The present invention also provides use of the controlled release fertilizers in lawns (especially golf course) and ornamental plant.
The present invention is accomplished by the following procedures:
1. Synthesization of the limited water-soluble compounds containing nitrogen, phosphorus, potassium, magnesium and trace elements, e.g., zinc, manganese, etc., which are essentially phosphates of metals having the formula:
M'MPO.sub.4,
in which M is K, Na or NH4, M' is Mg, Ca, Zn, Mn, Cu or Fe.
The compositions of these compounds are shown in Table 1.
                                  TABLE 1                                 
__________________________________________________________________________
The compositions and solubilities of the limited-soluble compounds        
                                     solubility                           
                                     at room                              
               molecular                                                  
                     composition %   temperature                          
No.                                                                       
   compounds   weight                                                     
                     N  P.sub.2 O.sub.5                                   
                           K.sub.2 O                                      
                              MgO                                         
                                 other                                    
                                     g/100gH.sub.2 O                      
__________________________________________________________________________
 1 MgHPO.sub.4.3H.sub.2 O                                                 
               174.33                                                     
                     -- 40.72                                             
                           -- 23.12                                       
                                 --  0.025                                
 2 MgNH.sub.4 PO.sub.4.H.sub.2 O                                          
               155.27                                                     
                     9.02                                                 
                        45.69                                             
                           -- 15.65                                       
                                 --  0.014                                
 3 MgNH.sub.4 PO.sub.4.6H.sub.2 O                                         
               245.27                                                     
                     5.71                                                 
                        28.92                                             
                           -- 9.91                                        
                                 --  0.018                                
 4 ZnNH.sub.4 PO.sub.4                                                    
               178.3 7.85                                                 
                        39.92                                             
                           -- -- Zn 36.6                                  
                                     0.015                                
 5 MnNH.sub.4 PO.sub.4.H.sub.2 O                                          
               185.97                                                     
                     7.58                                                 
                        38.18                                             
                           -- -- Mn29.5                                   
                                     0.0031                               
 6 CaHPO.sub.4.2H.sub.2 O                                                 
               172.10                                                     
                     -- 41.25                                             
                           -- -- --  0.025                                
 7 CaK.sub.2 (SO.sub.4).sub.2.3H.sub.2 O                                  
               328.3 -- -- 28.69                                          
                              -- S 19.5                                   
                                     0.25                                 
 8 KMgPO.sub.4.H.sub.2 O                                                  
               176.27                                                     
                     -- 42.27                                             
                           26.72                                          
                              22.88                                       
                                 --  limited-soluble                      
 9 KCaPO.sub.4.H.sub.2 O                                                  
               191.97                                                     
                     -- 36.96                                             
                           24.53                                          
                              -- --  limited soluble                      
10 FMP         not constant                                               
                     -- 18 0.5                                            
                              12 --  0.0016                               
11 MgO         40.32 -- -- -- 100                                         
                                 --  0.00062                              
12 Mg(OH).sub.2                                                           
               58.34 -- -- -- 60.13                                       
                                 --  0.0009                               
13 3MgCO.sub.3.Mg(OH).sub.2.3H.sub.2 O                                    
               365.37                                                     
                     -- -- -- 44.12                                       
                                 --  0.04                                 
__________________________________________________________________________
The compounds in Table 1 are all known compounds.
Compounds 1-9 in Table 1 can be prepared by phosphoric acid, sulfuric acid, magnesium oxide, magnesium carbonate, calcium oxide, ammonium phosphate, calcium carbonate, ammonium bicarbonate, zinc sulfate, manganese sulfate, potassium chloride or potassium sulfate according to literatures (such as "Inorganic Chemical Compound Synthesis Handbook" Vol. 1-2, edited by Japanese Chemistry Society, "The production and application of phosphates", pages 112-372). For example, when magnesium oxide is reacted with phosphoric acid, and the first and second hydrogen ions of the acid are completely neutralized (pH=2), a suspension of MgHPO4.3H2 O is formed, which is further neutralized with ammonia to form a mixture of MgHPO4.3H2 O and MgNH4 PO4 .H2 O. An example listed in literature is as follows:
47.5 kg of magnesium oxide (85% in purity, industrial grade) was added to 355 kg of phosphoric acid (20% of P2 O5, industrial grade) . The reaction temperature was maintained at 85° C. for 0.25 hour with continuously stirring to form a suspension of MgHPO4.3H2 O and MgO with a pH value of 2. Continuously adding with ammonia the pH value of the suspension was increased to a level from 5 to 6, resulting in a suspension containing MgNH4 PO4 . H2 O and MgO, after filtering, obtaining a coating material of a controlled release fertilizer which contains nitrogen 10.2 wt %, P2 O5 45.9 wt %, MgO 26.2 wt % ("Phosphate and Compound fertilizer", No.4, pp19-20, 1989). Compounds 10-12 in Table 1 are commercially available products and compound 13 is formed by the absorption of carbon dioxide in air on magnesium hydroxide. The plant nutrients, such as nitrogen, phosphorus, potassium, magnesium, zinc and manganese contained in the above compounds with limited solubilities in water can be slowly released in water. The coating layers composed of the above compounds are in an amount of 35 to 68 percent on the basis of the total weight of the fertilizer.
2. Selection of the binders. The binders used comprise non-reactive binders and reactive binders. The non-reactive binders can be a mixture of sulfuric acid or phosphoric acid at certain concentrations with monoammonium phosphate, diammonium phosphate or ammonium bicarbonate, which mixture is bound with compounds having various solubilities and coated on the surface of water-soluble granular fertilizer layer by layer. On the other hand, the binders can be reactive binders which can react with single fertilizer such as urea, monoammonium phosphate, diammonium phosphate, ammonium bicarbonate, ammonium sulfate, potassium chloride or potassium sulfate to form limited-soluble compounds . Two kinds of reactive binders can be selected, one kind is organic binders such as formaldehyde, starch and carboxy methyl cellulose, which can condense with urea to form limited-soluble compounds containing nitrogen. Urea has a property of condensation-addition with various organic compounds (UREA, ITS PROPERTIES AND MANUFACTURE). Now an example is taken for illustrating the condensation reaction of urea with formaldehyde. 0.04 kg hexamethyleneamine was added to 3kg formaldehyde solution (37 wt %), after completely dissolved, 0.8 kg urea was added with continuously stirring and heating until said urea was completely dissolved. The mixture was heated to a constant temperature of 60° C. for 15 min., then the temperature was maintained at 92° C. for 70 min., so that urea-formaldehyde condensation was taken place, 0.4 kg aqueous urea solution (50 wt %) was added in 30 min. to keep on the reaction. After 20 min., the reaction was stopped. The reaction solution was cooled to 60° C. and then a 10% aqueous sodium hydroxide solution was added to neutralize the urea-formaldehyde resin solution till pH=7, and then the reaction mixture was cooled to room temperature to obtain a semi-transparent slurry, which was then mixed with water in a ratio of 1:5 to get urea-formaldehyde resin binders. The other kind of binders is inorganic binders such as phosphoric acid or sulfuric acid used alone or mixed with monoammonium phosphate, diammonium phosphate, ammonium bicarbonate or ammonium sulfate, said binders can react with magnesium oxide, calcium oxide, zinc sulfate, manganese sulfate, potassium sulfate or potassium chloride to obtain compounds 1-9 in Table 1. The concentrations and formulations of the selected binders are shown in Table 2. The amount of the binders is 5-10% on the basis of the total weight of fertilizer.
              TABLE 2                                                     
______________________________________                                    
The specification and concentration of binders                            
                            concentration or                              
No.   Name of binders       formulation                                   
______________________________________                                    
OA    formaldehyde solution 36˜40% (wt)                             
OB    2-10% carboxymethyl cellulose: urea                                 
                            1:0.2˜0.4                               
OC    amylum solution       2˜10% (wt)                              
IA    phosphoric acid       30˜60% P.sub.2 O.sub.5                  
IB    sulfuric acid         6˜30% (wt)                              
IC    30-60% phosphoric acid: ammonium                                    
                            1:0.3˜0.6 (wt)                          
      bicarbonate                                                         
ID    6-30% sulfuric acid: monoammonium                                   
                            1:0.5˜0.7 (wt)                          
      phosphate or diammonium phosphate                                   
______________________________________
3. The solubilities of limited-soluble compounds 1-10 in Table 1 can be adjusted by adding inorganic additives such as ammonium sulfate, ammonium chloride, ammonium nitrate and magnesium sulfate into the coating layer and the release rates of nutrients in the fertilizer can be controlled. The amount of regulator is 0-5% on the basis of the total weight of fertilizer. For example, the solubility of MgNH4 PO4.6H2 O in Table 1 can be adjusted by adding ammonium sulfate as shown in Table 3. When no ammonium sulfate is added, 80% nitrogen in the fertilizer can be released out within 140 days. If adding 5% ammonium sulfate, the release period is only 70 days.
The solubilities of the limited-soluble compounds can also be changed by adjusting the pH values of the salts contained in the coating layers so as to control the release rates of the fertilizers. For example, the solubilities of FMP listed in Table 1 will change along with the pH values of the solutes, as shown in Table 4.
              TABLE 3                                                     
______________________________________                                    
The effection of ammonium sulfate on the                                  
solubility of MgNH.sub.4 PO.sub.4.6H.sub.2 O, 25° C.               
Concentration of (NH.sub.4).sub.2 SO.sub.4                                
               The solubility of MgNH.sub.4 PO.sub.4.6H.sub.2 O           
(g/100 g solution)                                                        
               (g/100 g solution)                                         
______________________________________                                    
0              0.018                                                      
1.25           0.1415                                                     
2.50           0.1876                                                     
5.0            0.2493                                                     
10.00          0.3535                                                     
______________________________________                                    

              TABLE 4                                                     
______________________________________                                    
The effect of pH on the solubility of FMP, 15%                            
magnesium sulfate solution (wt %)                                         
______________________________________                                    
pH        6.0   6.5   7.0 7.5 8.0 8.5 9.0 9.5  10.0 10.5                  
Solubility(wt %)                                                          
          9.5   7.8   6.6 5.6 5.4 5.3 3.8 0.28 0.03 0.013                 
______________________________________
Usually, the dissolution condition, i.e. the pH value is controlled to be more than 7 to decrease the solubilities of the limited soluble compounds in Table 1 and thus prolong the release time of nutrients. On the contrary, if the pH value of the solution is less than 7, then the release of the nutrients can be accelerated.
4. Treatment of the toppest layer of the coating layers can increase the density of the coating layers and decrease the hydrophilicity of the coating layers. Therefore, powder is applied on the surface of the coating layer. The powder used comprises fine magnesium oxide powder(<0.075 mm), which absorbs carbon dioxide from air to form compound 13 in Table 1 with smooth and fine shells. Alternatively, a calcium carbonate stearate powder (a water proof and insulated powder material whose preparing method can be found in Chinese Patent CN 91105131.7) is applied or a organic silicone is coated on to form a hydrophobic layer. The amount of the powder and hydrophobic layer applied is 2-5% by weight of the total fertilizer.
As stated above, the controlled release fertilizer according to the present invention can be manufactured by using granular water-soluble fertilizer such as urea, ammonium nitrate monoammonium phosphate, diammonium phosphate, potassium chloride, potassium sulfate and other compound fertilizer as nucleus, and coating on the nucleus with compounds containing nitrogen, phosphorus, potassium, magnesium and trace elements and having different limited solubilities layer by layer; or coating on the nucleus with limited soluble compounds which are formed by the reaction between a reactive binder and a single fertilizer during coating process. The number of coating layers are not less than 2, and preferable 3-5 so that the coating layers have a desirable thickness and different release rate. The solubility of limited-soluble compound can be changed by regulating the composition and pH value of coating layers, by which nutrient-releasing rate can be controlled to a release period of 60-240 days (the time required to release 80% nutrients). A controlled release fertilizer containing 30-50 wt % nitrogen, phosphorus pentoxide, potassium oxide and magnesium oxide can be manufactured optionally. Analysis with a scanning electroscope found that the cross section of coating layers was composed of dense amorphous compounds.
The controlled release fertilizer is essentially composed of nucleus and coating layers, the amount of nucleus is 20-50% by weight of the total mass, while the amount of coating layer is 50-80% by weight of the total mass. And the coating layer is comprised of a limited-soluble compound, an adjustment agent, a powder and a binder, which are 35-70%, 0-5%, 2-5% and 5-10% by weight of the total fertilizer respectively most of which are plant nutrients.
EXAMPLE
The following examples will illustrate the present invention in detail (The following parts referred to are all in weight portions).
Example 1
35 parts of granular urea was put into a special CCF granulator (China patent number: ZL892 14248.0), and preheated to 60° C. by blowing hot air (70° C.) heated by an electric heater. Then 1.3 parts formaldehyde (37 wt. %) solution containing hexamethyleneamine was sprayed into the granulator by an atomizer, after the granular urea was wetted, 3.6 parts powder urea was continuously added during the spraying of formaldehyde to form the first coating layer of urea-formaldehyde which was 5% by weight of the fertilizer; 17 parts reactive magnesium oxide and 7 parts monoammonium phosphate powder were added to the granules having the first coating layer by means of IC binder (which was prepared, as shown in Table 2, by adding 5 parts 40% phosphoric acid (based on P2 O5) to 2.6 parts ammonium bicarbonate), to provide the second coating layer containing ammonium magnesium phosphate, which was 26.6% by weight of the fertilizer; and then the third coating layer containing magnesium potassium phosphate, which was 26% by weight of the fertilizer, was formed by using a blend solution of 20% sulfuric acid and 40% phosphoric acid (based on P2 O5) in a ratio of 7:3 as binder, and continuously adding 5 parts monoammonium phosphate and 21 parts potassium chloride powder to the granules having the second coating layer. Finally, 5 parts calcium carbonate stearate was added to provide a hydrophobic layer which was 5% by weight of the total fertilizer. The final product was dried at 70° C. until the water content was less than 2%, and packed up after cooling to obtain a controlled release fertilizer with four coating layers. Measurment with a scanning electroscope found that the average diameter of nucleus was 2,300 μm, and the average total thickness of the four coating layers was 740 μm, and the average diameter of the fertilizer granule was 3780 μm. The composition of the fertilizer was N19%, P2 O5 10%, K2 O 12%, MgO 10%. Analysis by x-ray diffraction proved that the coating layer contained MgO, NH4 MgPO4.6H2 O, Mg(OH)2, KMgPO4.6H2 O, KCaPO4.H2 O (see FIG. 2).
Example 2
10 parts sulfuric acid (10% in concentration ) was placed into an acid-proof reaction tank, to which 5 parts monoammonium phosphate powder was added gradually under continuously stirring at ambient temperature, standing for half an hour a binder solution (ID in table 2)was obtained; 33 parts of granular ammonium nitrate was placed into a granulator, into which binder ID was sprayed and 25 parts NH4 MgPO4.6H2 O were added to provide the first coating layer which was 27% by weight of the total fertilizer. To a solution containing 10 parts 5% carboxymethyl cellulose, 4 parts urea powder was added, the mixture was allowed to react for 3 hours to provide binder OB in Table 2. The second coating layer was formed by coating 16 parts synthesized KMgPO4.H2 O onto the granules having the first coating layer by means of binder OB, which was 17.7% by weight of the total fertilizer. The third coating layer was formed by coating with 16 parts FMP by means of 30 wt % sulfuric acid as binder, which was 18% by weight of the total fertilizer. Finally, a fine and close shell layer was formed by powdering on the surface of the fertilizer with 4 parts magnesium oxide powder. The final product was dried at 70 C until the water content was less than 2%, and then packed up after cooling to obtain a fertilizer containing N 13%, P2 O5 18%, K2 O 5% and MgO 3%.
The release rate of the fertilizer in soil was determined as follow:
For this procedure, a φ 75×9 cm plastic pot was filled with a simulated soil which was composed of equal parts by volume of vermiculite powder and peat in a particle-size less than 10 mesh. There were several dozens of φ 3 mm drainage holes at the bottom of the pot.
The fertilizer sample of example 2(3 g) was incorporated uniformly into the simulated soil. The medium was then surface irrigated with distilled water until the medium was nearly saturated, but with little or no leaching from the pot. The whole installation was sealed and held at a constant temperature of 20° C. After a period of time, the saturated solution was extracted and analyzed for the N content, and resaturated with distilled water. The various release rates at different time can be measured in this way. The release rates curves was shown in FIG. 3.
Effect of the Fertilizer of the Invention
The main advantages of the fertilizer according to the present invention are as follows:
The Fertifizer provides 60, 90, 120 days longevity for nitrogen releasing, high utilization ratio of fertilizer, less frequent application and reduced labor costs;
it provides fully plant nutrients, need not blend with other fertilizers, it is easy for application, it feeds N, P, K and trace elements at one-shot according to the plant requirements;
it makes plants uniform growth, color and appearance, as it contains abundant magnesium which is necessary for plant growth and improves the synthesis of chlorophyll;
high safety for use and no pollutant, no plastic or wax contained in said fertilizer and all the components are plant nutrients;
flexible component and wide adaptability, can meet the needs of different regions and plants.
The fertilizer of the invention can be widely used in the fairways, roughs, parks, race courses, lawn tennis courts, sport grounds, turf farms and lawns.
______________________________________                                    
Application Experiment                                                    
          Lawn, sports general green                                      
                                  ornamental                              
Plant     ground, golf courts                                             
                       ground, parks                                      
                                  plant, flowers                          
______________________________________                                    
Rate (kg/100 m.sup.2)                                                     
          5-7          4-6        7-9                                     
______________________________________                                    

                                  TABLE 1                                 
__________________________________________________________________________
The present fertilizer Trial Results                                      
vs Scotts on Small Plots                                                  
Trial Set June 1, 1995                                                    
The present                                                               
      Lbs.N     July 1                                                    
                    Aug 1                                                 
                        Sept 1                                            
                            Oct 1                                         
                                Nov 1                                     
                                    Longevity                             
fertilizer                                                                
      per 1000 Ft.sup.2                                                   
            June 1                                                        
                30days                                                    
                    61days                                                
                        92days                                            
                            122days                                       
                                153days                                   
                                    days                                  
__________________________________________________________________________
18-6-12                                                                   
      1.0#  Set 9   10  10  7   5   122                                   
22-2-10                                                                   
      1.0#  Set 10  10  10  8   6   122                                   
18-6-12                                                                   
      1.5#  Set 10  10  10  7   5   122                                   
22-2-10                                                                   
      1.5#  Set 10  10  10  9   7   153                                   
18-6-12                                                                   
      2.0#  Set 9   10  10  8   8   153                                   
22-2-10                                                                   
      2.0#  Set 10  10  10  9   8   153                                   
Scotts PolyS                                                              
      1.0#  Set 10  10  7   6   4   92                                    
21-3-20                                                                   
100% PolyS                                                                
      1.0#  Set 10  10  7   7   5   122                                   
26-4-12                                                                   
100% PolyS                                                                
      1.0#  Set 9   10  7   5   4   92                                    
21-0-20                                                                   
100% PolyS                                                                
      1.5#  Set 10  10  7   5   5   92                                    
21-3-20                                                                   
26-4-12                                                                   
      1.5#  Set 10  9   8   7   6   122                                   
21-0-20                                                                   
      1.5#  Set 10  10  7   5   5   92                                    
21-3-20                                                                   
      2.0#  Set 10  9   9   7   5   122                                   
26-4-12                                                                   
      2.0#  Set 10  10  10  7   5   122                                   
21-0-20                                                                   
      2.0#  Set 10  10  9   7   5   122                                   
__________________________________________________________________________
 Note:                                                                    
 (1) Overall evaluation 1-10 growth color density                         
 (2) Blue grass with come bent and rye                                    
 (3) Healthy turf                                                         
 (4) Good rainfall                                                        
 (5) Reapplication would occur at 7                                       
 (6) "The present fertilizer" in all tables was made according to example 
 of the invention. The type number "ab-c" means that the contents of      
 nitrogen, phosphorus and potassium are a%, b% and c% respectively. For   
 example "186-12" means the contents of nitrogen, phosphorus and potassium
 are 18%, 6% and 12% respectively. And the type number has the same meanin
 in comparable examples.
COMMENTS
(1) 1. 10 Measuring Scale
(2) 7. Pot Needs Reapplication
(3) Blue Rye Grass--Small amount of Bent and Fescue
(4) Non Irrigated--Good Rainfall During Trial
(5) Trial was to Evaluate Rates Difference over 120 days
(6) August And September where very Hot 90° F. to 100° F.
RESULT
(1) 1 pound of N per 1000 Sq Feet Provide good,
(2)1.5 pound of N per 1000 sq Feet Provided Fast Green Up
(3) 2 to 3 pound of N per 1000 sq Feet provide Excessivem Growth in His Hot time of the year
(4) High Rates 2 to 3 pound N Did not produce A Better Result over time
(5) No Burning was Seen on Any Plots
                                  TABLE 2                                 
__________________________________________________________________________
Tabulated From Field sheet-by                                             
D. Deirson-Rate Trial of the present fertilizer                           
Trail set 11/7/95                                                         
The present                                                               
       Lbs of N                                                           
             12/8/95                                                      
                  15/9/95                                                 
                       6/10/95                                            
                            4/11/95                                       
fertilizer                                                                
       Lbs/1000 ft                                                        
             (32 days)                                                    
                  (66 days)                                               
                       (87 days)                                          
                            (116 days)                                    
                                 Snow  Comment                            
__________________________________________________________________________
1 × 1000 sq ft                                                      
       1#    10   10   10   10   Grass stop                               
                                       Good growth                        
1 × 1000 sq ft                                                      
       1#    10   10   10   10   Growring                                 
1 × 100 sq ft                                                       
       1#    10   10   10   10   before snow                              
1 × 1000 sq f                                                       
       1#    10   10   10   10   all plots                                
                                 Remained                                 
1 × 1000 sq ft                                                      
       1.5#  10   10   10   10   Green Good first 60 days                 
1 × 1000 sq ft                                                      
       1.5#  10   10   10   10         Good even growth                   
1 × 1000 sq ft                                                      
       1.5#  10   10   10   10                                            
1 × 1000 sq ft                                                      
       1.5#  10   10   10   10                                            
1 × 1000 sq ft                                                      
       2#    10   10   10   10         Excessive                          
1 × 1000 sq ft                                                      
       2#    10   10   10   10         growth first 30 days               
1 × 1000 sq ft                                                      
       2#    10   10   10   10                                            
1 × 1000 sq ft                                                      
       2#    10   10   10   10                                            
1 × 1000 sq ft                                                      
       2.5#  10   10   10   10         Excessive growth                   
1 × 1000 sq ft                                                      
       2.5#  10   10   10   10         in first 60 days                   
1 × 1000 sq ft                                                      
       2.5#  10   10   10   10                                            
1 × 1000 sq ft                                                      
       2.5#  10   10   10   10                                            
1 × 1000 sq ft                                                      
       3#    10   10   10   10         No Burning                         
1 × 1000 sq ft                                                      
       3#    10   10   10   10         in first 30 days                   
1 × 1000 sq ft                                                      
       3#    10   10   10   10         Excessive growth                   
1 × 1000 sq ft                                                      
       3#    10   10   10   10                                            
__________________________________________________________________________

TABLE 3                                                                    
  - Trials of the present fertilizer compared with                         
  other controlled release fertilizer in USA                               
   Trail Conditions                                                        
  Trials on Grass in USA  Lbs of N Treated Evaluation Criterion            
   Location of  Grass   (Lbs/1000 area Irri-   Uniform Stress              
  No. Trial Place type Date Product ft.sup.2) (ft.sup.2) gated Color       
 Density growth Tolerance Comment                                          
  1 Bay area Alameda Blue 1/6/95 The present fertilizer 1.5 1000 .smallcir 
 cle. 10 9 9 9 1. The present fertilizer                                   
   California Golf Rye (31days) (20-2-10) 1.5 1000 ∘ 10 8 9 9  
 lasted 120 days effective                                                 
   119°30'W Club   IBDU (21-3-16)        2. IBDU lasted 90 days     
      37°30N   3/8/95 The present fertilizer 1.5 1000 ∘ 
  10 10 9 8 effective                                                      
      (93 days) (20-2-10) 1.5 1000 ∘ 7 9 9 5 3. No rainfall    
         IBDU (21-3-16)                                                    
      5/9/95 The present fertilizer 1.5 1000  9 8 8 8                      
      (120 day) (20-2-10) 1.5 1000  5 6 6 4                                
       IBDU (21-3-16)                                                      
  2 Tuf-Turf Land- Blue 6/7/95 The present fertilizer 3/4 1000 x 10 9 9 9  
 1. The present fertilizer                                                 
   Kansas scape Rye (30 days) (20-2-10) Scotts 3/4 1000 x 10 9 9 9 lasted  
 120 days effective                                                        
   94°38'W Co.   Poly-S (21-2-21)        2. Scotts longevity        
 lasted                                                                    
   39°07N   7/8/95 The present fertilizer 3/4 1000 x 9 9 9 9 60     
 days                                                                      
      (72 days) (20-2-10) Scotts 3/4 1000 x 7 7 8 7 3. Heavy rain 15 in.   
 in month                                                                  
       Poly-S (21-2-21)        reduced longevity of both                   
      10/9/95 The present fertilizer 3/4 1000  8 7 7  products.            
      (120 day) (20-2-10) Scotts 3/4 1000  5 5 5                           
       Poly-S (21-2-21)                                                    
  3 Nebraska Dokoto Blue 14/8/95 The present fertilizer 1.5 1000 .smallcir 
 cle. 8 7 7 7                                                              
   100°00'W City Rye  (20-2-10) 1.5 1000 ∘ 8 8 7 7      
       41°31'N    7WIR (16-2-13)                                    
       The present fertilizer 3/4 1000 ∘ 8 8 8 8               
       (20-2-10) 3/4 1000 ∘ 8 8 8 8                            
       7WIR (16-2-13)                                                      
       The present fertilizer 1 1500 ∘ 7 7 7 7                 
       (20-2-10)                                                           
       7WIR (16-2-13) 1 500 ∘ 6 6 6 6                          
       The present fertilizer 3/4 2000 x 5 6 5 5                           
       (20-2-10) 3/4 2000 x 5 6 6 5                                        
       7WIR (16-2-13)                                                      
  4 Texas Waco Burmu- 7/8/95 The present fertilizer 1.8 2000 ∘ 
  10 10 10  Product lasted in hot                                          
   94°54'W  da (34 days) (20-2-10)        condition 138 days        
 before                                                                    
   29°24'N   4/10/95 The present fertilizer 1.8 2000 ∘  
 10 10 10  cooling took place.                                             
      (95 days) (20-2-10)                                                  
      16/11/95 The present fertilizer 1.8 2000 ∘ 10 10 10      
          (138 day) (20-2-10)                                              
      10/8/95 The present fertilizer 1.5 6600 x 10 10 10 10 1. LUXACOTE    
 lasted                                                                    
      (30 days) (20-2-10) Scotts 1.4 10000 x 10 10 10 10 120 days and      
 still remained                                                            
       Poly-S (25-3-10) 3.0 5600 x 9 10 10 10 green.                       
       ONCE(34-4-7)                                                        
   Ollio urban Blue 14/9/95 The present fertilizer 1.5 6600 x 10 10 10 10  
 2. Cool weather slowed                                                    
   IIlinois Golf grass (65 days) (20-2-10) Scotts 1.4 10000 x 10 10 10 9   
 growth (grass).                                                           
    Club   Poly-S (25-3-10) 3.0 5600 x 10 10 10 10                         
       ONCE(34-4-7)                                                        
  5 89°00'W School Fescue 15/10/95 The present fertilizer 1.5 6600  
 x 10 10 10 10 3. Scott 100% Poly-S did                                    
   40°00'N football  (96 days) (20-2-10) Scotts 1.4 10000 x 10 10   
 9 9 not last 120 days as                                                  
    fields   Poly-S (25-3-10)        expected.                             
       ONCE(34-4-7) 3.0 5600 x 10 10 10 10                                 
      12/11/95 The present fertilizer 1.5 6600 x 9 10 9 9                  
       (20-2-10) Scotts 1.4 10000 x 7 8 7 7                                
      (123 day) PoIy-S (25-3-10) 3.0 5600 x 10 10 9 9                      
       ONCE(34-4-7)                                                        
  6 Carmel Terra Ftcue 11/7/95 The present fertilizer 1/2 1000      1.     
 Lasted 120 day.                                                           
   Indiana office   (20-2-10) 1 1000      2. Rich Grant reported           
    (trial by           that LUXACOTE was                                  
    Rich           effective for 120 day.                                  
    Grant)                                                                 
   86°15'W  Blue  The present fertilizer 1/2 1000      3. Trial     
 conducted in                                                              
   40°00'N  Rye  (18-6-12) 1 1000      landscape situation at back  
               of terra office.                                            
  7  Research  24/7/95 The present fertilizer 2 5000 ∘ 5 3 7   
 My understanding that LUXACOTE                                            
    station   (20-2-10)       maintained good performance untill           
       The present fertilizer 1 5000 ∘ 10 10 10 fall cool      
 season.                                                                   
       (20-2-10)                                                           
       50% Poly-S(24-4-16) 2 5000 ∘ 7 3 3                      
       50% Poly-S(24-4-16) 1 5000 ∘ 3 3 7                      
  8 Michigan Gay Bent 1/10/95 The present fertilizer 1 1000  9 9 9 9 1.    
 Evaluated after 90 days,                                                  
   86°54'W Lord Blue (60 day) (20-2-10)  Two      cool weather in   
 oct. stoped                                                               
   41°43'N Country     compete      grass growthlooked good         
           Club     Fairway      until snow.                               
               2. Provided equal results                                   
               after 90 days with 100%                                     
               Poly-S product                                              
               3. Would use again next                                     
               year. No burning or                                         
               darmage on bent fairway.

Claims (4)

We claim:
1. A controlled release granular fertilizer having water-soluble fertilizers as a nucleus and limited-soluble plant nutrient compounds as coating layers, wherein more than two coating layers of limited-soluble compounds are formed around the nucleus, by bonding the nucleus with the coating layers having various solubilties by means of an aqueous 6-30 wt % sulfuric acid or 30-60 wt % phosphoric acid (based on P2 O5) solution mixed with monoammonium phosphate, diammonium phosphate, or ammonium bicarbonate as a binder, and the release rates of the nutrient compounds are controlled by regulating the solubilities of the limited-soluble compounds.
2. A controlled release granular fertilizer having water-soluble fertilizers as a nucleus and limited-soluble plant nutrient compounds as coating layers, wherein more than two coating layers are formed around the nucleus by bonding the nucleus with the coating layers by means of an inorganic reactive binder comprising an aqueous 6-30 wt % sulfuric acid or 30-60 wt % phosphoric acid (based on P2 O5) solution alone or a mixture of an aqueous sulfuric acid or phosphoric acid solution mixed with monoammonium phosphate, diammonium phosphate, ammonium bicarbonate or ammonium sulphate, said limited-soluble plant nutrient compounds are formed by reacting compounds containing nitrogen, phosphorous, potassium, magnesium and trace elements selected from the group consisting of MgO, CaO, ZnO, MnSO4, KCL, and K2 SO4 with said inorganic reactive binder during coating; and the release rate of the nutrient compounds are controlled by regulating the solubilities of the limited-soluble compounds.
3. The controlled release fertilizer according to claim 1 or 2, wherein the solubilities of the limited soluble compounds are adjusted by adding at least one inorganic salt selected from the group consisting of ammonium sulphate, ammonium chloride, ammonium nitrate, and magnesium sulphate, and/or by regulating pH values of the coating layers.
4. The controlled release fertilizer according to claim 1 or 2, wherein the surfaces of the controlled release fertilizer are treated with silicone or calcium carbonate stearate to enhance the hydrophobicity of the coating layers, and magnesium oxide is used as a powder to smooth the surfaces.
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